As conventional light writing type projection displays, the following apparatuses are known. (1) REFERENCE I (G. Marie: Ferroelectrics, 1976, Vol. 10, pp. 9-14) discloses a light writing type projection display as shown in FIG. 8 hereof. It is arranged such that a DKDP (KD2PO4) crystal 251, a CaF.sub.2 holder 261, a dielectric mirror 17, a photoconductive layer 16, a pair of transparent electrodes 15 and Peltier cells 27 are sealed in a vacuum vessel 241. In FIG. 8, reference numeral 6 designates a pair of lenses, 28, a polarizing beam splitter, 29, a light source for display, 30, an object used as an input image, 291, a light source for illuminating the object, 31, an input light beam, 12, display light beam, 13, projected light beam, 33, a power source for driving the DKDP crystal 251 and the photoconductive layer 16, and 34, a switch.
In the described arrangement, the input light beam 31 emitted from the light source 291 such as an xenon lamp or halogen lamp for illumination, reaches the photoconductive layer 16 through the lens 6 and the transparent electrode 15. The photoconductive layer 16 changes its resistivity spatially in accordance with the intensity of the input image. Accordingly, the electric field distribution applied to the DKDP crystal 251 can undergo a spatial change when the driving power source 33 connected to the pair of transparent electrodes 15 is turned on and off by the switch 34. During this process, an applied electric field is converted into a spatial distribution of refractive indices of the DKDP crystal by the electrooptic effect thereof. On the other hand, the display light beam 12 emitted from the display light source 29 is polarized by the polarizing beam splitter 28, passes through the lens 6, the CaF2 holder 261 in the vacuum vessel 241, and the transparent electrode 15, illuminates the DKDP crystal 251, and is reflected on the dielectric mirror 17. After that, it is transmitted along the path in the opposite direction, passes the polarizing beam splitter 28, and is projected on a screen (not shown) as the projected light beam 13. (2) REFERENCE 2 (Shigeru Yoshikawa, Masakatsu Horie, Hideo Takahashi, and Takaki Shimura: Journal of the Institute of Electronics and Communication Engineers of Japan, Vol. J59-C, No. 5 (1976) pp. 305-312) discloses a projection type display as shown in FIG. 9. It has a dynamic scattering mode type nematic liquid crystal light valve 35 adhered to a cathode ray tube 3 with a fiber optic faceplate. In FIG. 9, reference numeral 36 designates a signal generator, 37, a power source for driving the liquid crystal light valve 35, 29, a light source, 6, lenses, 8, an ultraviolet light cut filter, 9, a mirror, 12, a display light beam incident on the liquid crystal light valve 35, 13, a projected light beam, and 14, a screen. In this described arrangement, the light beam emitted from the light source 29 passes through the lenses 6, the ultraviolet light cut filter 8, and is reflected on the mirror 9 to form the display light beam 12. Subsequently, it passes through the lens 6 and reaches the liquid crystal light valve 35. The projected light beam 13 emitted from the liquid crystal light valve 35 passes through the lens 6, and is projected onto the screen 14, thus being displayed as an image.
The dynamic scattering mode type nematic liquid crystal light valve 35 is arranged in such a manner that the following elements are integrally laminated in sequence as shown in FIG. 10: a transparent electrode 15 which is adhered to the fiber optic faceplate 2 of the cathode ray tube 3; a semitransparent electrode 38; an SeTe photoconductive layer 39; a wire plate 40; a spacer 41; nematic liquid crystals 42; a transparent electrode 15; and a glass substrate 19.
(3) REFERENCE 3 (A. G. Ledebuhr: SID 86 Digest (1986) pp. 379-382) discloses a projection type display as shown in FIG. 11. It has three cathode ray tubes 3 each having a fiber optic faceplate 2 and a liquid crystal light valve 43 that is adhered to a respective fiber optic face plate 2, two polarizing beam splitters 44, and two dichroic filters 45. In FIG. 11, reference numeral 11 designates input wires for feeding electric signals to the cathode ray tubes 3, 47, a light source, 48, a display light beam emitted from the light source 47, 46, a transparent plate for compensating the optical path length of the blue light, 49, an aperture, and 50, a projected light beam modulated by the three twisted nematic liquid crystal light valves 43.
In this arrangement, the display light beam 48 emitted from the light source 47 passes the mirror 9, the aperture 49, the mirror 9, and the lenses 6, thus reaching the pair of polarizing beam splitters 44, 44. Then the beam passes the mirrors 9 and the lenses 6, and is split into three beams by the pair of dichroic filters 45. The three beams enter the three twisted nematic liquid crystal light values 43. In addition, the three light beams modulated by the three twisted nematic liquid crystal light valves 43 are coupled into one light beam by the pair of dichroic filters 45, and it passes the lens 6, the mirror 9, the polarizing beam splitter 44, the aperture 49, the mirror 9, the lens 6, and the mirror 9, and is projected to a screen not shown in this figure as the projected light beam 50. Thus, an image is displayed.
Each liquid crystal light valve 43 is arranged by laminating the following elements into a unit as shown in FIG. 12: an alignment layer 51, a nematic liquid crystal layer 52, an alignment layer 51, a dielectric multilayer mirror 53, a light absorption layer 54, a CdS photoconductive layer 55, and transparent electrodes 15 attached to both ends of the laminated layers. In FIG. 12, reference numeral 41 denotes a spacer in which the nematic liquid crystals are retained by a peripheral seal, 20, an alternating-current power supply connected to the transparent electrodes 15, 19, glass plates which are attached to the outer side of each transparent electrode 15, 31, an input light beam, 12, a display light beam incident on the liquid crystal light valve 43, and 13, a projected light beam.
(4) REFERENCE 4 (J. Trias, W. Robinson, and T. Phillips: SID 88 Digest (1988) pp. 99-101) discloses a projection type display as shown in FIG. 13. In this display, a write light beam 57 emitted from an argon ion laser 56 is incident on a twisted nematic liquid crystal light valve 43 through a laser raster scanner 58. On the other hand, a display beam 12 emitted from a xenon light source 4 is incident on the other surface of the liquid crystal light valve 43 through a polarizing beam splitter 44, and the reflected light beam thereon, namely, the projected light beam 13 is projected onto a screen (not shown in this figure) through a projection lens 6, thus displaying an image. In FIG. 13, reference numeral 59 designates an input electric signal, and 60, laser raster scanner electronics for driving the laser raster scanner 58 in accordance with the input electric signal 59. (5) REFERENCE 5 (Y. Mori, Y. Nagae, E. Kaneko, H. Kawakami, T. Hashimoto and H. Shiraishi: Displays April (1988) pp. 51-55) discloses a projection type display as shown in FIG. 14. In this figure, a write light beams 62 emitted from laser diodes 61 are incident on smectic liquid crystal light valves 65 through an X-Y scanner 64. On the other hand, display beams 12 emitted from xenon light sources 4 are incident on the other surfaces of liquid crystal light valves 65 through dichroic prisms 66, and the reflected beams on the valves are projected onto a screen 14 through a projection lenses 67. In FIG. 14, reference numeral 68 designates a liquid crystal light valve drive circuit, 66', wavelength filters, 69, a f-0 lens, 63, a collimating lens, 70, a polarizing prism, 71, a beam splitter, 72, an X-Y scanner drive circuit, 73, a system control circuit, and 74, a laser diode drive circuit.
The smectic liquid crystal light valve 65 is arranged by laminating the following elements in sequence as shown in FIG. 15: a transparent electrode 15, an alignment layer 51, a smectic liquid crystal layer 75, an alignment layer 51, a metal mirror 76, a heat sinking layer 77, glass substrates 19 provided on both sides of the layer unit, and antireflection films attached to the outer surfaces of the glass substrates 19.
The conventional light writing type projection displays described above have the following disadvantages.
(1) The projection type display of REFERENCE 1, which is described in (1) above and is shown in FIG. 8, uses the electrooptic effect of the DKDP crystal 251, resulting in the following:
(1-1) It necessitates a polarizer and an analyzer such as polarizing beam splitter 28. This reduces the availability of the display light beam to less than 50%.
(1-2) The broad spectral width of the display light beam 12 will reduce the contrast ratio of the image.
(1-3) As the DKDP crystal 251 is made thinner, the resolution will be improved. This, however, is difficult beyond a certain limit because a bulk single crystal cannot be thinned beyond a certain thickness by polishing (about 100 .mu.m thick by current technique).
(1-4) It is difficult to obtain a DKDP crystal having a large area.
(1-5) It is difficult to display a high definition image because of the reasons described in (1-3) and (1-4).
(1-6) The Peltier cells 27 must be used to cool the DKDP crystal 251 to about -50.degree. C. This makes the arrangement complicated.
(1-7) The drive voltage is large.
Accordingly, the display of REFERENCE I is unsuitable for displaying a high resolution image.
(2) The projection type display of REFERENCE 2 which is described in (2) above, and is shown in FIGS. 9 and 10 presents the following problems because dynamic scattering mode type nematic liquid crystals are used as the light valve 35.
(2-1) The speed of response of the liquid crystals is very slow.
(2-2) The power consumption of the liquid crystals is large, and the life of the liquid crystals is short because the liquid crystals are subjected to current drive.
(2-3) It has disadvantages such as a low contrast ratio of the displayed image. Accordingly, the display of REFERENCE 2 is unsuitable for displaying motion images.
(2-4) In addition, it uses the wire plate 40, which reduces the resolution.
(3) The projection type display of REFERENCE 3 which is described in (3) above, and is shown in FIGS. 11 and 12 has the following problems because the liquid crystal light valve 43 uses the birefringence of the twisted nematic liquid crystals.
(3-1) The display has problems similar to those of (1-1), (1-3) and (1-4) with regard to the display described in (1).
(3-2) In addition, the variation of thickness of the liquid crystal layer must be restricted within about .+-.50 nm over the entire layer. This makes it extremely difficult to fabricate a liquid crystal light valve having a large area and of high, uniform quality.
(3-3) The speed of response of the liquid crystals and CdS photoconductive layer is slow.
Accordingly, the display of REFERENCE 3 is unsuitable for displaying a high resolution motion image.
(4) The projection type display of REFERENCE 4 which is described in (4) above, and is shown in FIG. 13 has the following problems because it uses the liquid crystal light valve 43 like that used in the display of (3) above.
(4-1) The display has problems similar to those of (3-1), (3-2) and (3-3) with regard to the display described in (3).
(4-2) In addition, the write light source 56 and the beam splitter 44 become more complicated.
(4-3) The laser raster scanner 58 makes the write light beam 57 perform two dimensional scanning by using a traveling-wave lens using the accoustooptic effect. This produces higher order diffraction light around a condensing spot, decreasing the resolution.
Accordingly, the display of REFERENCE 4 is unsuitable for displaying high resolution motion images.
(5) The projection type display of REFERENCE 5 which is described in (5) above, and shown in FIGS. 14 and 15 operates on the following principle: it makes the write light beams 62 scan the smectic liquid crystal light valves 65; converts the smectic liquid crystals retained in the liquid crystal light valves 65 from the homogeneous state to the scattered state by using the thermal energy of the write light beams 62; and transmits or scatters the display light beams 12. This poses the following problems.
(5-1) Although the resolution is high, the speed of response is very slow. For example, it takes tens of seconds or about a minute to display a piece of a still image.
(5-2) It is difficult to display a gray scale image, that is, it is difficult to achieve full-color display.
(5-3) The beam scanner 64 must perform high precision scanning.
Accordingly, the display of REFERENCE 5 is unsuitable for displaying motion pictures.